Electroluminescent (EL) devices such as light emitting diode (LED) are opto-electronic devices which radiate light on the application of an electrical field. Organic materials including both polymers and small molecules have been used to fabricate LEDs. LEDs fabricated from these materials offer several advantages over other technologies, such as simpler manufacturing, low operating voltages, and the possibility of producing large area and full-color displays. Organic polymers generally offer significant processing advantages over small molecules especially for large area EL display because polymer films can be easily produced by casting from solutions.
Conjugated polymers such as poly(phenylvinylene) (PPV) were first introduced as EL materials by Burroughes et al in 1990 (Burroughes, J. H. Nature 1990, 347, 539-41). Other conjugated polymers include polydialkylfluorene (PF) (Ohmori, Y. et al Jpn. J. Appl. Phys. Part 2 1991, 20, L1941-L1943), poly(p-phenylene) (PPP) (Grem, G. et al Adv. Mater. 1992, 4, 36-7), and poly(thiophene). However, PPVs and their derivatives are among the most studied conjugated polymers because of their great potential applications in various areas including LED, photodiodes, organic transistors, and solid state laser materials. Electron donor such as alkoxy substituted PPVs show higher efficiencies than unsubstituted ones in LED applications. Amine groups are stronger electron donors than alkoxy groups, and amino-substituted PPVs have also been prepared to investigate the effect of amino groups on the LED efficiencies. However, only dialkylamines have been incorporated into PPV as substitutents (Stenger-Smith, J. D. et al Macromolecules 1998, 31, 7566-7569). It is known that dialkylamino groups are susceptible to oxidation.